table of contents
other versions
GLSAMPLERPARAMETER(3G) | [FIXME: manual] | GLSAMPLERPARAMETER(3G) |
NAME¶
glSamplerParameter - set sampler parametersC SPECIFICATION¶
void
glSamplerParameterf(GLuint sampler,
GLenum pname, GLfloat param);
void
glSamplerParameteri(GLuint sampler,
GLenum pname, GLint param);
PARAMETERS¶
samplerSpecifies the sampler object whose parameter
to modify.
pname
Specifies the symbolic name of a single-valued
sampler parameter. pname can be one of the following:
GL_TEXTURE_WRAP_S, GL_TEXTURE_WRAP_T, GL_TEXTURE_WRAP_R,
GL_TEXTURE_MIN_FILTER, GL_TEXTURE_MAG_FILTER,
GL_TEXTURE_MIN_LOD, GL_TEXTURE_MAX_LOD,
GL_TEXTURE_LOD_BIAS GL_TEXTURE_COMPARE_MODE, or
GL_TEXTURE_COMPARE_FUNC.
param
Specifies the value of pname.
C SPECIFICATION¶
void
glSamplerParameterfv(GLuint sampler,
GLenum pname,
const GLfloat * params);
void
glSamplerParameteriv(GLuint sampler,
GLenum pname,
const GLint * params);
PARAMETERS¶
samplerSpecifies the sampler object whose parameter
to modify.
pname
Specifies the symbolic name of a sampler
parameter. pname can be one of the following: GL_TEXTURE_WRAP_S,
GL_TEXTURE_WRAP_T, GL_TEXTURE_WRAP_R,
GL_TEXTURE_MIN_FILTER, GL_TEXTURE_MAG_FILTER,
GL_TEXTURE_BORDER_COLOR, GL_TEXTURE_MIN_LOD,
GL_TEXTURE_MAX_LOD, GL_TEXTURE_LOD_BIAS
GL_TEXTURE_COMPARE_MODE, or GL_TEXTURE_COMPARE_FUNC.
params
Specifies a pointer to an array where the
value or values of pname are stored.
DESCRIPTION¶
The texture minifying function is used
whenever the pixel being textured maps to an area greater than one texture
element. There are six defined minifying functions. Two of them use the
nearest one or nearest four texture elements to compute the texture value. The
other four use mipmaps.
A mipmap is an ordered set of arrays representing the same image at
progressively lower resolutions. If the texture has dimensions 2 n × 2 m,
there are max n m + 1 mipmaps. The first mipmap is the original
texture, with dimensions 2 n × 2 m. Each subsequent mipmap has dimensions
2 k - 1 × 2 l - 1, where 2 k × 2 l are the dimensions of the
previous mipmap, until either k = 0 or l = 0. At that point, subsequent
mipmaps have dimension 1 × 2 l - 1 or 2 k - 1 × 1 until the final
mipmap, which has dimension 1 × 1. To define the mipmaps, call
glTexImage1D(), glTexImage2D(), glTexImage3D(),
glCopyTexImage1D(), or glCopyTexImage2D() with the level
argument indicating the order of the mipmaps. Level 0 is the original texture;
level max n m is the final 1 × 1 mipmap.
params supplies a function for minifying the texture as one of the
following:
GL_NEAREST
As more texture elements are sampled in the minification process, fewer aliasing
artifacts will be apparent. While the GL_NEAREST and GL_LINEAR
minification functions can be faster than the other four, they sample only one
or four texture elements to determine the texture value of the pixel being
rendered and can produce moire patterns or ragged transitions. The initial
value of GL_TEXTURE_MIN_FILTER is
GL_NEAREST_MIPMAP_LINEAR.
GL_TEXTURE_MAG_FILTER
Returns the value of the texture element that
is nearest (in Manhattan distance) to the center of the pixel being
textured.
GL_LINEAR
Returns the weighted average of the four
texture elements that are closest to the center of the pixel being textured.
These can include border texture elements, depending on the values of
GL_TEXTURE_WRAP_S and GL_TEXTURE_WRAP_T, and on the exact
mapping.
GL_NEAREST_MIPMAP_NEAREST
Chooses the mipmap that most closely matches
the size of the pixel being textured and uses the GL_NEAREST criterion
(the texture element nearest to the center of the pixel) to produce a texture
value.
GL_LINEAR_MIPMAP_NEAREST
Chooses the mipmap that most closely matches
the size of the pixel being textured and uses the GL_LINEAR criterion
(a weighted average of the four texture elements that are closest to the
center of the pixel) to produce a texture value.
GL_NEAREST_MIPMAP_LINEAR
Chooses the two mipmaps that most closely
match the size of the pixel being textured and uses the GL_NEAREST
criterion (the texture element nearest to the center of the pixel) to produce
a texture value from each mipmap. The final texture value is a weighted
average of those two values.
GL_LINEAR_MIPMAP_LINEAR
Chooses the two mipmaps that most closely
match the size of the pixel being textured and uses the GL_LINEAR
criterion (a weighted average of the four texture elements that are closest to
the center of the pixel) to produce a texture value from each mipmap. The
final texture value is a weighted average of those two values.
The texture magnification function is used
when the pixel being textured maps to an area less than or equal to one
texture element. It sets the texture magnification function to either
GL_NEAREST or GL_LINEAR (see below). GL_NEAREST is
generally faster than GL_LINEAR, but it can produce textured images
with sharper edges because the transition between texture elements is not as
smooth. The initial value of GL_TEXTURE_MAG_FILTER is GL_LINEAR.
GL_NEAREST
GL_TEXTURE_MIN_LOD
Returns the value of the texture element that
is nearest (in Manhattan distance) to the center of the pixel being
textured.
GL_LINEAR
Returns the weighted average of the four
texture elements that are closest to the center of the pixel being textured.
These can include border texture elements, depending on the values of
GL_TEXTURE_WRAP_S and GL_TEXTURE_WRAP_T, and on the exact
mapping.
Sets the minimum level-of-detail parameter.
This floating-point value limits the selection of highest resolution mipmap
(lowest mipmap level). The initial value is -1000.
GL_TEXTURE_MAX_LOD
Sets the maximum level-of-detail parameter.
This floating-point value limits the selection of the lowest resolution mipmap
(highest mipmap level). The initial value is 1000.
GL_TEXTURE_WRAP_S
Sets the wrap parameter for texture coordinate
s to either GL_CLAMP_TO_EDGE, GL_MIRRORED_REPEAT, or
GL_REPEAT. GL_CLAMP_TO_BORDER causes the s coordinate to be
clamped to the range -1 2N 1 + 1 2N, where N is the size of the texture in the
direction of clamping. GL_CLAMP_TO_EDGE causes s coordinates to be
clamped to the range 1 2N 1 - 1 2N, where N is the size of the texture in the
direction of clamping. GL_REPEAT causes the integer part of the s
coordinate to be ignored; the GL uses only the fractional part, thereby
creating a repeating pattern. GL_MIRRORED_REPEAT causes the s
coordinate to be set to the fractional part of the texture coordinate if the
integer part of s is even; if the integer part of s is odd, then the s texture
coordinate is set to 1 - frac s, where frac s represents the
fractional part of s. Initially, GL_TEXTURE_WRAP_S is set to
GL_REPEAT.
GL_TEXTURE_WRAP_T
Sets the wrap parameter for texture coordinate
t to either GL_CLAMP_TO_EDGE, GL_MIRRORED_REPEAT, or
GL_REPEAT. See the discussion under GL_TEXTURE_WRAP_S.
Initially, GL_TEXTURE_WRAP_T is set to GL_REPEAT.
GL_TEXTURE_WRAP_R
Sets the wrap parameter for texture coordinate
r to either GL_CLAMP_TO_EDGE, GL_MIRRORED_REPEAT, or
GL_REPEAT. See the discussion under GL_TEXTURE_WRAP_S.
Initially, GL_TEXTURE_WRAP_R is set to GL_REPEAT.
GL_TEXTURE_BORDER_COLOR
The data in params specifies four
values that define the border values that should be used for border texels. If
a texel is sampled from the border of the texture, the values of
GL_TEXTURE_BORDER_COLOR are interpreted as an RGBA color to match the
texture's internal format and substituted for the non-existent texel data. If
the texture contains depth components, the first component of
GL_TEXTURE_BORDER_COLOR is interpreted as a depth value. The initial
value is 0.0, 0.0, 0.0, 0.0.
GL_TEXTURE_COMPARE_MODE
Specifies the texture comparison mode for
currently bound textures. That is, a texture whose internal format is
GL_DEPTH_COMPONENT_*; see glTexImage2D()) Permissible values
are:
GL_COMPARE_REF_TO_TEXTURE
GL_TEXTURE_COMPARE_FUNC
Specifies that the interpolated and clamped r
texture coordinate should be compared to the value in the currently bound
texture. See the discussion of GL_TEXTURE_COMPARE_FUNC for details of
how the comparison is evaluated. The result of the comparison is assigned to
the red channel.
GL_NONE
Specifies that the red channel should be
assigned the appropriate value from the currently bound texture.
Specifies the comparison operator used when
GL_TEXTURE_COMPARE_MODE is set to GL_COMPARE_REF_TO_TEXTURE.
Permissible values are:
where r is the current interpolated texture coordinate, and D t is the texture
value sampled from the currently bound texture. result is assigned to R
t.
Texture Comparison Function | Computed result |
GL_LEQUAL | <div> result = 1.0 0.0 r <= D t r > D t </div> |
GL_GEQUAL | <div> result = 1.0 0.0 r >= D t r < D t </div> |
GL_LESS | <div> result = 1.0 0.0 r < D t r >= D t </div> |
GL_GREATER | <div> result = 1.0 0.0 r > D t r <= D t </div> |
GL_EQUAL | <div> result = 1.0 0.0 r = D t r ≠ D t </div> |
GL_NOTEQUAL | <div> result = 1.0 0.0 r ≠ D t r = D t </div> |
GL_ALWAYS | <div> result = 1.0 </div> |
GL_NEVER | <div> result = 0.0 </div> |
NOTES¶
ERRORS¶
ASSOCIATED GETS¶
SEE ALSO¶
COPYRIGHT¶
Copyright © 2010 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.05/30/2012 | [FIXME: source] |